The present invention relates to a method and apparatus for detecting solids and foreign matters that might be present in transparent containers filled with a liquid. More particularly, the present invention relates to an improved method and apparatus for detecting automatically such undesirable minute foreign matters as glass chips, fibers, and dust that might be present in such transparent, closed containers as vials, ampoules, and infusion solution bottles in which is filled a liquid, by measuring the change of transmitted light with a group of small light receivers, wherein the improvement comprising the means that eliminates from the detecting visual field the signals only from the swirling surface, which occurs when the object (such as ampoule) to be detected is rotated and then brought to a stop quickly, while following the swirling liquid level as it is restored gradually, whereby detection can be performed immediately after the stop of rotation, without waiting until the liquid surface becomes completely stationary, although the transmitted light is changed by the liquid surface.
Heretofore, a method as shown in FIG. 1 has been in use for detection of foreign matters. In this method, an ampoule (1) to be inspected is placed on a rotating device, turned at a high speed by motor (2), and then stopped quickly by a brake. Light from lamp (4) is irradiated to ampoule (1) through condenser lens (5) and a vertical slit (not shown) as indicated by chain lines. The irradiated light passes through the liquid and hits small light receivers (7.sub.1), (7.sub.2), . . . , (7.sub.n) constituting light detector (7), through image forming lens (6). The magnitude of transmitted light changes if there are foreign matters that are suspending and swirling with the content liquid. The presence of foreign matters is judged according to the extent of decrease of transmitted light.
Such a conventional method has a disadvantage that if the surface (8) of the content liquid coincides with the light receiving position, the light incident on that part becomes dim on transmission through the liquid surface, causing the small light receivers to receive extremely decreased light, and as the liquid surface moves up and down, the quantity of light incident upon the small light receiver fluctuates and this fluctuation is processed in the same manner as for the change in the quantity of light caused by foreign matters and the resulting signals are mistaken for the signals caused by foreign matters. In order to eliminate such a disadvantage, it is necessary to exclude the signals corresponding to the liquid surface (8) from the signals to be inspected. This has been accomplished in the conventional method by carrying out measurements while foreign matters are still suspended and swirled together with the content liquid after the swirl in the ampoule has become moderate and the liquid surface (8) has been restored to the upper level. This has still another disadvantage that heavy or relatively large foreign matters such as glass chips tend to settle as soon as the rotating ampoule is brought to a stop, and therefore they would have deposited on the bottom of the container (1) and would not be detected as foreign matters if measurement is carried out after the swirl has become moderate and the liquid surface (8) is restored.
The measurement is made more complex by the fact that the restoration of the swirling liquid surface (8) varies delicately depending on the viscosity of the content liquid, the quantity of the liquid filled, the shape and size of the container (1), the speed of rotation, and the timing of stop. There is variation among ampoules even for the same solution.
Therefore, the conventional method in which measurement is carried out sequentially from bottom to top according to a standardized, preset program, does not comply with the delicate ampoule to ampoule difference and tends to give incorrect results. In addition, the conventional method is inefficient if different programs are to be set for respective kinds of ampoules and liquids.
In order to obviate these disadvantages, we have completed this invention which is characterized by that the detection is accomplished as the liquid surface is restored, with the light receivers corresponding to the liquid surface being omitted in the detection.
A single photoelectric element is not suitable as a light detector which is to be used for the light receiver of the apparatus according to this invention. This is because foreign matters to be detected are extremely small as compared with the detecting visual field and the difference in the magnitude of photoelectric current which is caused by the presence of foreign matters is too small to detect foreign matters with reasonable sensitivity. A satisfactory detection with a sufficient S/N ratio can be accomplished for any kind of foreign matters, whatever shape they might be--particulate or fibrous, if we install a multiplicity of small light receivers, each having a certain light receiving area equal to or smaller than the projected area of individual particles of foreign matters and measure the intensity of the beam of passing light with the small light receivers which varies in proportion with the projected area of foreign matters.
According to the method of this invention, the swirling liquid surface in each ampoule is caught by the small light receivers of the light detector and output signals from the small light receivers corresponding to the swirling liquid surface are excluded from other signals for measurement, and thus continuous measurement is possible for individual ampoules even though the time for the swirling liquid surface to be restored differs depending on the viscosity of the liquid, the shape and size of the container, and the quantity of liquid filled in the container. Therefore, there is no need for setting programs, and effective, error-free measurement can be accomplished.
The light that has passed the liquid surface is extremely dimmed as compared with one that has passed the content liquid. Using this it is possible to inhibit the small light receivers corresponding to the liquid surface from issuing output signals and to permit the other small light receivers to issue digital output signals, if the signal from the small light receivers is lower than the arbitrarily set standard value. Signals from the small light receivers are filtered by capacitors to remove DC components and only signals due to moving foreign matters are taken up as AC components. Such signals are compared with the arbitrarily set standard value by comparators, and those signals exceeding such standard value are issued for defective ampoules. The output due to foreign matters and the output not corresponding to the liquid surface undergo AND operation to eliminate signals resulting from the liquid surface so that only output signals resulting from foreign matters are obtained as outputs that actuate the solenoid for removing defective ampoules.
Incidentally, in the method and apparatus of this invention, the detection visual field covers the upper part of the ampoule in which there is no liquid, but this has nothing to do with the detection of foreign matters because the light that passes the empty part is more intense than the light that passes the liquid and the intensity remains constant.